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M4 motorway



{{UK motorway routebox| motorway= M4
length-mi= 189.5length-km= 305.0direction= East - Weststart= London
Chiswick		destinations= West London (Hounslow)
Heathrow Airport
Slough
Maidenhead
Reading
Newbury
Swindon
Chippenham
Bristol
Newport
Cwmbran
Cardiff
Bridgend
Port Talbot
Neath
Swansea
Llanelli		end= Pont Abraham servicesopening-date= 1961completion-date=1996junctions= 4B -

M25 motorway
8/9 -

A308(M) motorway
8/9 -

A404(M) motorway
10 -

A329(M) motorway
19 -

M32 motorway
20 -

M5 motorway
21 -

M48 motorway
22 -

M49 motorway
23 -

M48 motorway
29 -

A48(M) motorway

The M4 motorway is a motorway in England and Wales linking London and west Wales via Bristol. Other major places directly accessible from M4 junctions are Reading, Swindon, Newport, Cardiff and Swansea.

Notes

In the construction of the section around Cardiff in 1980, numbers were set aside for intermediate interchanges that were not built at the time. 33 had been set for the link road to the west (A4232), 32 for the A470, with 31 intended for the A469 to Caerphilly, and 30 for the great "Hook Road" - a plan which was later shelved. Junction 30 was later added to serve the link road in the east, which will eventually form a ring road from junctions 33 to 30, via Cardiff Bay. Number 31 remains unused as of 2005, and there are no immediate plans to build a junction with the A469.

Contrary to popular belief, junction 39 does exist, however, it consists of a single slip road completing the missing movement onto the westbound carriageway from the A48 at junction 38, thus there is no exit from the motorway at this junction.

Junction 41 refers to two different junctions in the two different directions, their movements not complementary. In the westbound direction, 41 is indicated as a spur leading to the roundabout in Briton Ferry formerly known as 41A, and the original bridge over the River Neath, which would allow access onto the stretch of the M4 from junction 43 westward. In the eastbound direction, 41 is indicated as an exit-only route to the A48 towards Port Talbot. As a result, it is possible in both directions to travel almost 2 miles (3 km) in the same direction having both joined and subsequently left the motorway at "junction 41".

Special features

The M4 has several special features. In London, the eastbound (London-bound) carriageway has a bus lane from junction 3 until the elevated section. This lane caused much controversy when it was created. However, the bus lane has (counterintuitively) improved traffic flow onto the 2-lane elevated section which follows it; there is some evidence that the original plan simply involved closing one lane from J3 to the elevated section to prevent congestion caused by the filtering of three lanes of traffic into two (the motorway is already temporarily down to two lanes at J3 because the left lane at J3 is exclusively for traffic leaving the motorway, so the effect of the bus lane is to make the 3-to-2 transition seamless). Making the "spare" lane available for buses - and now taxis - was an afterthought.

The elevated section in West London, built in the 1960s, is mostly directly above the A4 and extends over parts of Brentford's Golden Mile. This section has a heated road surface to reduce icing in winter.

25 miles (40 km) west, the motorway is the only one in the UK to feature a 'dual-numbered' junction. Junction '8/9' is the turn off for Maidenhead, Berkshire.

The M4 crosses the River Severn via a toll bridge, the second of only two on the UK motorway network — the first was the original Severn Bridge (the original route of the M4, now the M48). (The London Orbital M25 motorway requires the use of the toll-collecting Dartford Crossing to complete a circuit, but the crossing itself is downgraded to an "A" road to allow use by local traffic).

There is a slip road west of the A34 to Newbury from the eastbound carriageway which leads to RAF Welford. This slip road is marked by a red and white roadsign.

Speed checks

Speed checks are carried out between junction 14 and junction 18 (in both directions). These are carried out by police camera vans situated on bridges over the motorway. These measure the speed of vehicles using laser detection equipment. The introduction of these measures proved controversial and resulted in a public protest, involving a go-slow of several hundred vehicles along the affected sections of the motorway during April 2005.{{

cite news		url=http://news.bbc.co.uk/1/hi/england/wiltshire/4498551.stmpublisher=BBC Newstitle=Drivers hold M4 speed camera demodate=April 30, 2005

Traffic heading into London travels at a maximum speed of 60 mph (97 km/h) after the Heathrow turnoff, the limit is enforced by cameras. The elevated section is also enforced by speed cameras at 40 mph (64 km/h). Traffic heading out of London is limited to 40 mph (64 km/h) on the elevated section, but there are no cameras.

Speed checks are also carried out by mobile Safety Camera Partnership vans on the toll plaza on the Welsh side of the M4 after the Second Severn Bridge. There are also mobile camera vans on sections of the M4 between the toll plaza and Cardiff.

The section between junction 40 and junction 41 has a maximum speed of 50 mph (80 km/h), and is enforced by a permanent speed camera (Gatso), to be found near junction 41 (in both directions).

Junctions

The M4 between junctions 22 and 23, crossing the River Severn from England to Wales on a cable-stayed bridge (the Second Severn Crossing). Wales is seen in the distance.

Motorway.m4.arp.750pix.jpg

The M4 near Bristol (England) between junctions 19 and 20, looking west towards Wales.

{| border=1 bgcolor=#fffff8 cellpadding=3 style="margin-left:1em; color: black; border-collapse: collapse;"|- align="center" bgcolor="0080d0" style="color: white;font-size:120%;"		 M4 Motorway|- align="center" bgcolor="000000" style="color: white"EastboundJunction-London A41Start of motorway>-A4 North Circular A406 South Circular A205 Chiswick A315 2Brentford A4>- align="center" Heston services|-Heathrow Terminal 4 & Cargo, Hayes, Harrow, Hounslow A3123Heathrow Terminal 4 & Cargo, Hayes, Harrow, Feltham A312>-Heathrow Terminals 1, 2 & 3 (A4) Uxbridge (A408)4Heathrow Terminals 1, 2 & 3 (A4) Uxbridge (A408)>-Heathrow Terminal 4 & Cargo, Gatwick Airport, Watford, Oxford M254BHeathrow Terminal 4 & Cargo, Gatwick Airport, Watford, Oxford M25>-Colnbrook, Langley A4 Eton, Datchet B4705Colnbrook, Langley A4 Datchet B470>-Slough A355 Windsor A3226Slough A355 Windsor A322>-Slough (A4)7Slough (A4)>-High Wycombe, Henley A404(M) Maidenhead A308(M)8/9High Wycombe, Henley A404(M) Maidenhead A308(M)>-Reading, Wokingham, Bracknell A329(M)10Reading, Wokingham, Bracknell A329(M)>-Basingstoke, Reading, A3311Basingstoke, Reading, A33>- align="center" Reading services|-Reading, Theale A412Reading, Theale A4>-Newbury, Oxford A34 & Chieveley services13Newbury, Oxford A34 & Chieveley services>-Hungerford, Wantage A33814Hungerford, Wantage A338>- align="center" Membury services|-Swindon A419 Marlborough A346Oxford (A420)15Swindon, Gloucester A419Marlborough A346>-Swindon A310216Swindon A3102>-Chippenham A350 Cirencester A42917Chippenham A350 Cirencester A429>- align="center" Leigh Delamere services|-Bath, Stroud A4618Bath, Stroud A46>-Bristol M3219Bristol M32>-The SOUTH WEST, Bristol, The MIDLANDS, Gloucester M5 (Almondsbury Interchange)20Bristol, Exeter, The MIDLANDS, Gloucester M5 (Almondsbury Interchange)>-No exit21Chepstow M48>-Avonmouth M49 The SOUTH WEST, Bridgwater, Exeter (M5)22Avonmouth M49>- align="center" Second Severn Crossing|-Chepstow M4823No exit>-Magor, Caldicot B4245 & Magor services23AMagor, Caldicot B4245 & Magor services>-Newport A48 & B4237, Monmouth A449, The MIDLANDS (M50)24Newport A48 & B4237, Monmouth A449>-No exit25Caerleon B4596>-No exit25ANewport, Cwmbran A4042>-Newport, Cwmbran, Caerleon A405126Newport A4051>-High Cross B459127High Cross B4591>-Newport A48 Risca, Brynmawr A46728Newport A48 Risca, Brynmawr A467>-No exit29Cardiff A48(M)>-Cardiff A423230Cardiff A4232>-Cardiff, Merthyr Tydfil A47032Cardiff, Merthyr Tydfil A470>-Cardiff & Airport, Barry, Penarth A4232 & Cardiff West services33Cardiff & Airport, Barry, Penarth A4232 & Cardiff West services>-Llantrisant, Rhondda A411934Llantrisant, Rhondda A4119>-Pen-coed A47335Bridgend, Pen-coed A473>-Bridgend A4061 Maesteg A4063 & Sarn Park services36Bridgend A4061 Maesteg A4063 & Sarn Park services>-Porthcawl, Pyle A422937Porthcawl, Pyle A4229>-Port Talbot A4838Port Talbot A48>-No exit39No exit>-Port Talbot A410740Port Talbot A4107>-Port Talbot A4841Briton Ferry A48>-Swansea A483 Briton Ferry A4842Swansea A483>-Neath, Merthyr Tydfil A46543Neath, Merthyr Tydfil A465>-Swansea A4844Swansea A48>-Swansea, Pontardawe A406745Swansea, Pontardawe A4067>-Swansea B448946Swansea B4489>-Swansea A483 & Swansea West services47Swansea A483 Pontarddulais A48 & Swansea West services>-Pontarddulais, Llanelli A413848Pontarddulais, Llanelli A4138
Start of motorway49Carmarthen A48 Ammanford A483 & Pont Abraham services''

See also

*M4 corridor
*List of motorways in the United Kingdom

References

External links

*CBRD Motorway Database - M4
*British Road Database: Motorways - M4 Junction 8/9






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